High performance demands made on modern day motorcycles which may be used for pleasure driving or racing on a wide variety of surfaces under varying conditions, dictates the importance of being able to have a shock absorber whose function may be effectively and selectively varied for handling, comfort and safety of the motorcycle rider for the motorcycles with which shock absorbers are used.
In operation, a shock absorber must necessarily effectively absorb the high impact forces encountered during high speeds on regular as well as irregular riding surfaces. The shock absorber must also permit the wheels to return to the ground or surface as quickly as possible without inducing bounce so as to maintain optimum traction conditions for effective control of the vehicle, for example, motorcycle.
Although it is ordinarily the load spring which actually absorbs the forces of impact, it is the action of the damping unit, such as the shock absorber, which controls the rate of wheel travel during the compression and rebound phases of the shock absorber. In present day shock absorber design, the rebound rate is made slower than the compression rate in order to provide faster impact absorption on compression of the shock absorber and in a slower return on the rebound to prevent too rapid recoil or a catapult effect.
It has been found that even with the same load spring and motorcycle, different damping compression and rebound rates are required to achieve optimum performance of the vehicle, or for example motorcycle, for the different terrains encountered.
Most shock absorbers have fixed ratios between compression and rebound damping. Some shock absorbers have adjustable rebound damping, but the shock absorber must be removed or partially disassembled from the motorcycle with which it is used in order to allow for adjustment.
While there is one prior art device known of, as set forth in U.S. Pat. No. 3,848,710 to Thompson and Cowan, the device shown therein allows for external adjustment without disassembly of a shock absorber, but only for fluid flow during one functional mode of the shock absorber. In contradistinction, the present invention is directed to a shock absorber wherein control of fluid flow through a piston of the shock absorber may be had during the compression and rebound phases of the shock absorber. Additionally, the metering means used to obtain different flow rates through the compression orifice and the rebound orifice of the shock absorber are independently adjustable from an external position, so that the shock absorber need not be disassembled in order to achieve adjustment for varying surfaces or terrains with which the shock absorber of the invention may be used.